Trommel equipment is widely used for sorting material by size in various industries including construction, waste disposal, landscaping, and building demolition. It is also used by aggregate producers. Trommel screens are typically cylindrical in shape, open at both ends, and are rotated while in use. A trommel screen is also typically inclined, so that material naturally tends to travel from the higher end to the lower end. The material to be processed is dumped into the higher end of a trommel screen and rotation causes the material to tumble towards the lower end. Some of the material (i.e. the “fines”) falls down through the trommel screen. The balance, being generally coarse material, is discharged out the lower end.
Conventional portable trommel equipment typically comprises a rotary trommel, an input conveyor, and a fines conveyor. These are mounted together on a chassis, which is typically provided with wheels at one end and a “fifth wheel” at the other, for connection to a conventional tractor unit. The input conveyor serves to feed the trommel with materials that are deposited on it. The fines conveyor collects screened material (i.e. the fines) falling through the trommel screen, and can extend the length of the machine from underneath the trommel to a discharge end.
One example of a portable trommel is described in U.S. Pat. No. 5,819,950. This patent describes a portable trommel having a stockpiling conveyor mounted on the chassis. The stockpiling conveyor comprises a lower end adapted to receive screened material from the fines conveyor and an upper end for discharging screened material to form a stockpile. The stockpiling conveyor can have two parts, which are moveable between a first, extended, operational position, and a second, retracted position for transportation. Accordingly, a “folding” of the stockpiling conveyor is effected when the two parts thereof are moved into the retracted position, which may enable the portable trommel to be transported more readily on ordinary roads.
In one embodiment of the invention described in U.S. Pat. No. 5,819,950, the portable trommel is equipped with activation means adapted to displace the two parts of a stockpiling conveyor between the operational and retracted positions. In this embodiment, the activation means comprises a pair of hydraulic pistons and cylinder assemblies, and a corresponding pair of mechanical linkages on either side of the stockpiling conveyor.